Laelaps

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The skeleton of “Nichollsiaborealis. The left forelimb and scapula were accidentally destroyed during excavation, but otherwise the skeleton was kept intact. From Druckenmiller & Russell 2008.

Last week I mentioned that a very well-preserved Early Cretaceous plesiosaur named “Nichollsiaborealis* was recently described in the journal Palaeontographica Abteilung A, and one of the authors was kind enough to send a scan of the paper to me. What follows is a brief summary of the significance of the find.

*I put the genus name in quotes as Nichollsia is occupied by an isopod, and a new genus name for this plesiosaur is going to be published soon.

According to the authors of the paper, the majority of plesiosaur fossils come from Jurassic deposits in Europe and from Late Cretaceous beds in North America, leaving some temporal and geographical gaps in the distribution of the ancient marine reptiles. “Nichollsia,” by contrast, was discovered in an open pit that was being mined and is of an Early Cretaceous age, being found in marine deposits of what once was the Boreal Sea during the time it was extending south to connect with the Western Interior Seaway. Unfortunately the skeleton incurred some damage during the excavation process, losing the left forelimb and scapula, but otherwise the skeleton was extraordinarily well-preserved and was excavated in one block to preserve as much of the material as possible.

The skeleton itself appears to be from a juvenile or young adult individual that was not fully-grown. The bones that make up the vertebrae were not fully fused together, which is indicative of immature specimens. At 2.6m in length, this was no giant, but although this specimen was not from a mature adult (and therefore differences in the skeleton were checked to make sure they weren’t just the result of ontogeny) it was unique enough to merit a new moniker.

The majority of the paper is a general description of the features of the skeleton, but at least one aspect of the find caught my attention. The skeleton was subjected to a CT scan to try and detect any other features that might not immediately be visible. The scan revealed that a sclerotic ring was preserved in the left eye, a rare find, although the ring in the right eye was either lost or obscured the a burrow made by a small creature in the orbit. This feature is known from other plesiosaurs, but being that is is delicate it is not often preserved. The function of the sclerotic ring is still somewhat unclear, but it seems to have a role in supporting the eye and has been found in a variety of organisms (including birds, dinosaurs, and ichthyosaurs).

As for what “Nichollsia” was eating, its teeth suggest that it had the “traditional” plesiosaur diet of fish and cephalopods, its dentition being useful to pin & grab rather than rip & tear. “Nichollsia” also had a number of smoothed stones, or gastraoliths, in its stomach, which could have aided in the digestion of fish or regulating buoyancy as the plesiosaur swam through the Cretaceous seas. Although many artistic representations often show the neck of this animal having snake-like flexibility (plesiosaurs were described early on as being like a snake threaded through a turtle), in life they could not coil their necks in upon themselves or into loops. Overall they were probably not particularly fast swimmers, nor did they habitually grab pterosaurs from the sky, but the fact that there are several different body forms exhibited in plesiosaurs suggests that there were different ways for each variety to hunt and capture prey.

Where “Nichollsia” fits in terms of relationships to other plesiosaurs is a bit murky, however. It is similar to the recently described Umoonasaurus from Australia and Leptocleidus from Europe, all three exhibiting a mix of characters that are present in both the short-necked pliosaurs and the long-necked plesiosaurs. Given that plesiosaur phylogeny is a bit contentious at the moment, the authors refrain from attributing “Nichollsia” to a family group until things become a little better resolved. They do note “Nichollsia” does show a general correspondence to the short-necked plesiosaurs of the group Polycotylidae, which contains plesiosaurs like Dolichorhynchops, although there are a number of features expressed by “Nichollsia” that do not seem to fit with other known members of the Polycotylidae.

Just as we can expect to hear more about “Nichollsia” in the future, we can also expect to see more plesiosaurs described from the same location. In the conclusion of the paper the others reference other long- and short-necked plesiosaurs found at the same mine, so it sounds like the Syncrude pit is a very productive location that may yield other well-preserved specimens. For now, though, “Nichollsia” is significant for where and when it lived, and will certainly be useful in redrawing the relationships among plesiosaurs.

References;

Druckenmiller, P.S.; Russell, A.P. (2008) “Skeletal anatomy of an exceptionally complete specimen of a new genus of plesiosaur from the Early Cretaceous (Early Albian) of northeastern Alberta, Canada.” Palaeontographica Abteilung A, Vol. 283, p. 1-33

Comments

  1. #1 Zach Miller
    March 31, 2008

    Pat is from Alaska (up in Fairbanks)! Sounds like a cool plesiosaur.

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